Elastic nonwoven fabrics can be employed in a variety of environments such as bandaging materials, garments, diapers, support clothing, and personal hygiene products because of their breathability as well as their ability to allow more freedom of body movement than fabrics with more limited elasticity.
Nonwoven fabrics are commonly made by melt spinning thermoplastic materials. Such fabrics are called "spunbond" materials and methods for making spunbond polymeric materials are also well known in the field. While spunbond materials with desirable combinations of physical properties, especially combinations of softness, strength and durability, have been produced, significant problems have been encountered.
One problem is attributed to the characteristic "sticky" nature of the elastomers typically employed in producing nonwoven materials. Processes such as spunbonding which employ air drawing can be particularly effected. For example, turbulence in the air can bring filaments into contact and these "sticky" filaments can then adhere to one another. This stickiness proves to be especially troublesome during winding of the webs into rolls. The layers of web adhere to one another, a phenomenon known as "blocking".
Certain methods have been developed in an attempt to overcome this problems. One such method is described in U.S. Pat. No. 4,720,415, where an elastic web is stretched and nonelastic fabrics are calendar bonded to the web, which is then allowed to contract. Such a "stretch-bonded" laminate has extensibility determined by the original extent of the stretching during the lamination process. Any attempt to stretch the laminate beyond this limit is resisted by the nonelastic layers on both sides of the elastic web.
Another method for overcoming the "stickiness" of elastic webs is to laminate one or two layers of an extensible nonwoven fabric to the web in the unstretched state. The extensible fabrics can typically be extended up to 200% or more in one or two directions, but they possess little recovery force after the extension. Therefore, the elastic web component provides the recovery force in the resulting laminate. Examples of such arrangements are described in U.S. Pat. Nos. 4,981,747, and 5,543,206 as well as PCT WO 96/16216.
Yet another method which attempts to overcome the inherent "stickiness" of webs made from elastic filaments involves mixing nonelastic fibers among the elastic filaments, so that the resulting composite fabric does not have a high level of stickiness. Such fabrics can be more easily unwound from rolls. A convenient way of mixing elastic filaments and inelastic fibers is by the "hydroentanglement" process. This approach is described in U.S. Pat. Nos. 4,775,579 and 4,939,016. Another approach to mixing involves blending an air stream containing inelastic staple fibers with an air stream containing elastic filaments. This approach is described in U.S. Pat. No. 4,803,117.
While these methods are capable of decreasing the effect of the stickiness of the elastic filaments, they introduce a significant complication into the process for producing an elastic nonwoven fabric. Such complications can result in a significant addition to the cost of the resulting fabric.
In addition to the "stickiness" issue, attempts to provide spunbond elastomeric polymers have faced problems such as breakage or elastic failure of the strand during extrusion and/or drawing. Broken strands can clog the flow of filaments and/or mesh with other filaments, resulting in the formation of a mat of tangled filaments in the web.
While the art has sought to address the foregoing problems, it is clear that the results have, at best, been mixed.
Separately, attempts have been made to influence the properties of fabrics by modifying the content of the fibers. For example, it has been known "combine" polymers in bi-and multicomponent fibers.
Bi-component fibers were the subject of U.S. Pat. Nos. 5,352,518 and 5,484,645. The '518 patent illustrates a composite elastic filament in a sheath-core arrangement in which the sheath component is composed of a thermoplastic polymer, such as a polyamide, polyester or polyolefin while the core is composed of an elastomer, such as a polyurethane or polyester elastomer.
The use of multi-component strands is also found in U.S. Pat. No. 5,405,682 to Shawyer et al. This patent discloses filaments that are employed in the production of nonwoven fabrics and which include, as one component, a blend of polyolefin and elastomer material. Once again, the polymeric strands are preferably in a sheath and core arrangement in which the sheath comprises a blend of a polyolefin and a thermoplastic elastomeric polymer.
It is also known to employ mixtures of fibers in forming nonwoven fabrics. See, for example, U.S. Pat. Nos. 3,353,345 and 4,107,364.
U.S. Pat. No. 3,353,345 illustrates an inelastic blend of stable fibers that includes both hard staple fibers that are essentially inelastic and bi-component staple fibers that comprise both a hard inelastic fiber component and one or more elastomeric fiber components. The two components are arranged such that the hard component will separate from the elastic component when exposed to heat or hot wet conditions without tension.
U.S. Pat. No. 4,107,363 relates to a nonwoven fabric produced by at least two types of fibers or filaments, one of which is elastomeric and another being elongated but non-elastic. In particular, this patent discloses an arrangement which includes a random web on a continuous filament cloth.